1. Field of the Invention
The present invention relates to measurement and characterization of soil moisture content, and more particularly, to methods and systems for using electromagnetic radiation to determine soil moisture content over a large geographic area.
2. Description of the Related Art
Land surface moisture measurements are central to our understanding of the earth's water system. Among many potential applications, accurate and up-to date knowledge of surface moisture content enables more accurate model-based weather/climate predictions, and assists with management of weather-related phenomena such as flash flood forecasting. Further, knowledge of surface moisture variation has numerous agricultural applications, such as assisting with more effective crop management and drought monitoring.
While small-scale local soil moisture measurement systems have been developed, there is a clear need for improved soil moisture estimates on both regional and continental scales. Particularly missing in prior applications are methods or systems for obtaining continuous, wide-area, near-surface (5-200 cm) water storage measurements. This is exemplified by the fact that the North American Land Data Assimilation System (NLDAS) relies on multiple models driven by meteorological data to extrapolate water storage, but the extrapolated results from these models are not in good agreement.
Several techniques have been used in the past to obtain soil moisture estimates. One approach includes the use of local probes to measure soil moisture at fixed positions. This is impractical for wide-area coverage. Also, since the rainfall rates in convective storms vary significantly over distances of a few kilometers, soil moisture estimates derived from point measurements may not accurately reflect broad regional conditions. Wide-area estimates can be derived by coupling rainfall estimates and hydrological models, but both the models and the rainfall estimates are poor, and lead to extremely large errors. Currently, space-based passive microwave measurements provide an alternative option, but even this approach suffers from limited penetration depth and/or signal attenuation due to vegetation. Also, there are currently no plans for continuous geostationary satellite monitoring of land surface moisture, at least over North America. Therefore, there is a need for improved systems and methods to obtain wide-area, continuous soil moisture estimates.